Aqueous lyotropic liquid crystal (LLC) assemblies have garnered widespread attention in disparate areas of chemistry, by virtue of their utility in highly selective chemical separations such as water desalination and selective ion-transporting membranes, as templates for mesoporous inorganic materials, as media for biophysical studies of transmembrane proteins (“cubic lipidic phases”), and as therapeutic nucleic acid delivery vehicles. LLCs form by the concentration-dependent supramolecular self-organization of amphiphilic molecules in water into soft materials having distinct hydrophilic and hydrophobic nanoscale domains (approximately 7 to 100 Å) with long-range periodic order. LLCs typically exhibit ordered phases such as lamellae (Lα), bicontinuous cubic (Q; e.g., double gyroid, double diamond, and “Plumber's Nightmare”), hexagonally packed cylinders (H), and discontinuous cubic (I; e.g., body-centered cubic) morphologies. High symmetry Q-phase assemblies, exemplified by the gyroid (G) phase, are particularly desirable for membrane applications by virtue of their interpenetrating aqueous and hydrophobic domains with tunable nanopore diameters (approximately 7 to 50 Å) and well-defined nanopore functionalities that percolate over macroscopic lengthscales. Q-phases typically exist only in limited water concentration and temperature phase windows, due to the fact that their interfaces substantially deviate from a constant mean interfacial curvature. While “critical packing parameter” models enable correlations of amphiphile structure with the formation of constant mean curvature Lα, H, and I phases, these models fail to provide reliable and general molecular design criteria for amphiphiles that form non-constant mean curvature Q phases. It was recently reported that small molecule quaternary ammonium, phosphonium, and imidazolium Gemini amphiphiles, derived from dimerizing single-tail surfactants with an alkyl spacer through the ionic headgroup, exhibit a greater tendency to form G phase LLCs. The notion that Gemini architectures universally form bicontinuous cubic LLC morphologies remains an untested amphiphile design principle.
In order to advance applications of LLC assemblies for membrane filtration, ion conduction, and other transport processes, increased attention has been devoted to polymerizable triply periodic multiply continuous LLCs. The weak non-covalent forces stabilizing these supramolecular assemblies render them soft and mechanically inferior. Also, their concentration dependent phase behavior limits their potential utility in solution-phase molecular sieving for aqueous separations. By installing polymerizable functionalities in the surfactant structure, a LLC assembly may be covalently fixed in place by thermal or photo-polymerization to yield a robust polymeric network with retention of the triply periodic structure. The low dimensionality of Lα-phases and H-phases requires domain alignment at macroscopic lengthscales in order to achieve transport through either the hydrophilic or hydrophobic domains of an LLC. However, the high symmetry and three-dimensional structural periodicity of the interpenetrating domains of triply periodic multiply continuous phases result in percolating domains that do not require alignment. By virtue of their construction, the hydrophilic and hydrophobic domains of LLCs have dimensions d of approximately 5-100 Å with domain interfaces that are decorated with well-defined chemical functionalities. The dimensions of the water-filled channels are approximately one order of magnitude smaller than those in nanoporous block copolymers (d approximately 50-1000 Å), enabling applications including water desalination, ultrafiltration, selective ion transport.
What is needed are additional molecules that can assemble to form LLC assemblies.